An originating telephone communication switch belonging to a long distance exchange carrier provides telephone service instructions which enable a customer, known as an alternate destination redirection (ADR) customer, to have calls redirected from a primary destination to a secondary destination, when the primary destination is busy or the call has not been answered within a predetermined interval, called a ring no answer (RNA) condition.
The primary destination of the ADR customer, in many circumstances, is directly connected to a terminating switch which is included in a long distance exchange carrier network, in other words, a switching network owned by the long distance carrier. If this is the case, the terminating switch provides an indication to the originating switch whether a busy or RNA condition exists at the primary destination. Accordingly, the originating switch determines whether redirection of the call to the secondary destination is appropriate.
When a call to the primary destination must be routed through a local exchange carrier network, in other words, a switching network owned by a local exchange carrier, all calls from the terminating switch of the long distance carrier to called destinations in the local network are routed by a local egress switch in the local network. An ADR customer whose call is routed first through the long distance network and then to the local network which includes the primary destination is known as a switched egress customer.
Sometimes, the local switch of the local carrier does not provide sufficient terminating line status information in the form of either a busy or free indication to the terminating switch of the long distance carrier, and ultimately the originating switch of the long distance carrier, when the primary destination in the local network is busy. Normally, without either a busy or free indication, the ADR feature of busy redirection to a secondary destination cannot be implemented, because the originating switch cannot determine whether or not the call is busy and thus redirect the call.